This section provides background information related to the present disclosure which is not necessarily prior art. This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
Lean burn combustion strategies are an attractive option to increase the thermal efficiency of gasoline spark ignition internal combustion engines, but engine design remains challenging due to the flammability limits of the fuel/air mixture. Turbulent jet ignition originating from a combustion pre-chamber can help address mixture flammability limits by ejecting high enthalpy and highly reactive jets into the main combustion chamber, thereby enhancing the combustion in the main chamber. However, appropriate mixture conditions must be achieved in the pre-chambers for this strategy to be successful. Pre-chambers have been studied extensively in the past, specifically related to compression ignition engines, as a capable technology to improve in-cylinder combustion robustness. Past learnings of traditional pre-chamber technologies related to heat transfer losses and mixture stratification have specifically guided the sizing, shape, orientation, and number of pre-chambers. The engine design developed in this work proposes a new approach to pre-chamber design that is enabled by advancements in numerical simulations, computational resources, fuel injection hardware, and manufacturing techniques. Specifically, the design considers a combustion system where fuel is injected into the main chamber and a fuel/air mixture is passively introduced into an adjacent pre-chamber connected to the main chamber whereby spark electrodes located in the pre-chambers are capable of igniting the localized mixture within the pre-chamber.
In some embodiments, pre-chambers are a means to enable lean burn combustion strategies which can increase the thermal efficiency of gasoline spark ignition internal combustion engines. A new engine concept is evaluated in this work using computational simulations of non-reacting flow. The objective of the computational study was to evaluate the feasibility of several engine design configurations combined with fuel injection strategies to create local fuel/air mixtures in the pre-chambers above the ignition and flammability limits, while maintaining lean conditions in the main combustion chamber. The current work used computational fluid dynamics to develop a novel combustion chamber geometry where the flow was evaluated through a series of six design iterations to create ignitable mixtures (based on fuel-to-air equivalence ratio, ϕ) using fuel injection profiles and flow control via the piston, cylinder head, and pre-chamber geometry. The desirable and undesirable features that guided the design progression are presented. Major combustion chamber design iterations involved changes to the pre-chambers position relative to the cylinder head deck plane, azimuthal orientation of the pre-chambers, and piston crown geometry. Further criteria were developed to assess the flow interaction with the nozzle connections to the pre-chambers. The modeling results indicated appropriate fueling strategies achieved near stoichiometric fuel-to-air equivalence ratios in the pre-chambers with lean fuel-to-air equivalence ratios in the main chamber. The results also demonstrated the utility of the flow-alignment and chamber filling criteria to select the nozzle design for the pre-chambers.
Lean burn combustion strategies are an attractive option to increase the thermal efficiency of gasoline spark ignition internal combustion engines, but engine design remains challenging due to the lean flammability limits of the fuel/air mixture. Lean after treatment strategies can be a concern; however, recent advances show considerable promise for effective emissions control for lean burn gasoline direct injection engines. Turbulent jet ignition originating from a combustion pre-chamber can help address mixture flammability limits by ejecting high enthalpy and highly reactive jets into the main chamber, enabling lean combustion in the main chamber. However, appropriate mixture conditions must be achieved in the pre-chamber for this strategy to be successful.
Pre-chambers have been studied extensively in the past, in particular for application in compression ignition engines, and pre-chambers have been successfully demonstrated as technology which can improve in-cylinder combustion robustness. Past learnings of pre-chamber technologies, including studies of the effects of heat transfer and mixture stratification, have guided the size, shape, orientation, and number of pre-chambers.
The engine concept presented in this work is based on a new pre-chamber engine design where the spark electrodes are located in the pre-chamber and a direct injection (DI) fuel injector is located in the main chamber. Supplemental fueling (e.g. DI or port fuel injection (PFI)) is used to create the initial fuel/air charge in the main combustion chamber. To the best of our knowledge, this approach differs from any pre-chamber engine designs previously considered. The design was enabled by advances in numerical simulations, computational resources, fuel injection hardware, and manufacturing techniques. Specifically, the objective of the design process documented here was to develop a combustion system where lean fuel-to-air equivalence ratios are created in the main chamber while near stoichiometric equivalence ratios are created in the pre-chambers using the DI fuel injector.
With the passing of the Clean Air Act of 1970 and the subsequent establishment of the Environmental Protection Agency, engine technologies offering significantly reduced tailpipe emissions started gaining major attention. Notably, gasoline pre-chamber engine concepts offered a promising solution to decreasing mobile sources of air pollution by increasing fuel efficiency and by decreasing engine-out emissions. Pre-chamber engine concepts are not a new technology to the automotive industry. H. R. Ricardo's internal combustion engine, documented in 1918, is the earliest pre-chamber concept found in the literature. The pollution regulations of the 1970's brought renewed focus on the pre-chamber engine concept from research institutions and industry. Most of the pre-chamber engine concepts suffered from atypical induction designs that required complicated valvetrain arrangements; however, recent advances in numerical simulations and computational resources allowed gasoline pre-chamber engine concepts to be systematically considered in new configurations. The comprehensive review by Toulson et al. outlined the progress of pre-chamber initiated combustion systems throughout history and provided sound engineering and scientific foundations for new engine designs which leveraged the best features of pre-chambers. Attard et al. demonstrated an auxiliary-fueled turbulent jet ignition pre-chamber concept in a GM Ecotec engine platform capable of achieving 42% peak net indicated thermal efficiency without the need for a complicated valvetrain induction system. In comparison, the standard GM Ecotec engine platform achieved a peak net indicated thermal efficiency of 37.9% in stoichiometric spark ignition mode of operation.
The work presented in this application focused on designing a prototype pre-chamber engine that reduces system complexity by eliminating the need for an auxiliary fuel injector located in the pre-chamber. Instead, the pre-chambers were designed to be fueled using an injection event from a fuel injector centrally mounted in the main combustion chamber (i.e. a gasoline DI system). This design concept leverages the advanced capabilities of modern fuel injectors and targets overall fuel lean operation. The technical approach used CFD to evaluate non-reacting in-cylinder flows of fuel and air achieved through different engine geometries. The designs were evaluated using metrics defined in the study to assess the efficacy of the flow at achieving the desired equivalence ratios in the pre-chambers and the main chamber.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
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